Shingled magnetic recording storage system

ABSTRACT

The disclosed technology includes methods and systems that reduce off-track write retry operations in shingled magnetic recording systems. In one implementation, the method includes writing data to an initial track, determining which side of the initial track is a shingled side, calculating a percentage of position error signal (PES) at a shingled side end of the initial track (PES1) when an off-track write operation occurs, determining whether the PES1 meets a first pre-determined threshold, continue writing data to a second track responsive to determining the PES1 is below a first pre-determined threshold, calculating a percentage of PES at a shingled side end of the second track (PES2), determining whether a combined value of PES1 and PES2 is above a second predetermined threshold to determine a probability value of the initial track being erased, and continue writing to a third track if the combined value is below the second predetermined threshold.

CROSS-REFERENCE

This application is a continuation application of U.S. patentapplication Ser. No. 15/720,486, filed Sep. 29, 2017, now U.S. Pat. No.10,xxx,xxx, the entire disclosure of which are incorporated herein byreference for all purposes.

BACKGROUND

As requirements for data storage density increase for magnetic media,cell size decreases. A commensurate decrease in the size of a writeelement is difficult because in many systems, a strong write fieldgradient is needed to shift the polarity of cells on a magnetizedmedium. As a result, writing data to smaller cells on the magnetizedmedium using the relatively larger write pole may affect thepolarization of adjacent cells (e.g., overwriting the adjacent cells).One technique for adapting the magnetic medium to utilize smaller cellswhile preventing adjacent data from being overwritten during a writeoperation is shingled magnetic recording (SMR).

SMR allows for increased areal density capability as compared toconventional magnetic recording (CMR) but at the cost of someperformance ability. As used herein, CMR refers to a system that allowsfor random data writes to available cells anywhere on a magnetic media.In contrast to CMR systems, SMR systems are designed to utilize a writeelement with a write width that is larger than a defined track pitch. Asa result, changing a single data cell within a data track entailsre-writing a corresponding group of shingled (e.g., sequentiallyincreasing or decreasing) data tracks.

SUMMARY

The disclosed technology includes methods and systems that reduceoff-track write retry operations in shingled magnetic recording systems.In one implementation, the data storage systems and methods write datato an initial track in a band of a shingled magnetic recording medium,calculate a percentage of position error signal (PES) at a shingled sideend of the initial track (PES1) when an off-track write operationoccurs, and determine whether the PES1 is above a first pre-determinedthreshold. If the PES1 is above the first pre-determined threshold, are-write operation is performed to the track or media cache. If thepercentage of PES1 is below the first pre-determined threshold, data iswritten to a second track, and a percentage of PES at the second track(PES2) is calculated at a shingled side end of the second track, and adetermination is made as to whether the combine value of PES1 and thePES2 is above a second pre-determined threshold to determine aprobability value of the initial track being erased. If the combinedvalue of the PES1 and the PES2 is above the second pre-determinedthreshold, data is re-written to the initial track or media cache. Ifthe combined value of the PES1 and the PES2 is below the secondpre-determined threshold, data is written to a third track.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. These andvarious other features and advantages will be apparent from a reading ofthe following Detailed Description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a block diagram of an example SMR data storage system,including a schematic diagram of example shingled tracks in the SMR datastorage system.

FIG. 2 is a schematic diagram of example shingled tracks in an SMR datastorage system.

FIG. 3 is a flowchart of example operations for an improved throughputprocess in an SMR data storage system.

FIG. 4 is a block diagram of an example computer system suitable forimplementing the technology disclosed herein.

DETAILED DESCRIPTION

The present disclosure is directed to data storage systems that reduceoff-track write retry operations to improve throughput in shingledmagnetic recording (SMR) systems. Several factors may impact throughputin SMR systems. For example, disc write retry operations can impactthroughput. When disturbances occur, off-track writes can occurfrequently and trigger write retry operations.

Disturbances such as impact shock and vibration can be a cause ofproblems in hard drive disc systems, particularly during writeoperations. If a disturbance occurs while data is being written to astorage medium, a write element may be knocked off of a target datatrack. As a result, data may be recorded incorrectly or becomecorrupted. Disturbances may be caused by a variety of forces, such as auser playing loud music from a laptop computer, vibrations due tocooling fans turning on or off, or external impact forces absorbed by anelectronic device.

If a disturbance occurs while data is being written to a storage medium,data may be recorded incorrectly or become corrupted. In some recordingsystems, storage space is statically mapped so that each data block(e.g., a sector) is associated with a logical address assigned by a hostcomputer. In these types of systems, a write operation affected by adisturbance can be retried at the statically mapped location until thewrite succeeds. However, write retries are time consuming, and may takea full spin period or revolution time of a magnetic media in the storagemedium. If the frequency of disturbance-related write errors is large,throughput performance can decrease. These challenges are magnified inSMR systems.

An SMR drive is a storage device that uses bands of overlapping tracksto increase storage density. In SMR, a new track may be written thatpartially overlaps a previously written track, creating a shingledaspect to the tracks. SMR leverages the fact that a width of a read headis typically narrower than the width of a write head. The storagedensity of an SMR drive is increased over conventional drives becausethe previously written tracks are thinner, allowing for higher trackdensity. In an SMR drive, a set of bands of overlapping tracks may beseparated by an isolation space, which serves to reduce the number oftracks that need to be rewritten when a shingled track is rewritten. InSMR, a write element may be large enough to affect two adjacent datatracks on a single pass. If the write element is displaced from a targetposition by vibrations, adjacent tracks on either side of a target trackcan be affected.

The present disclosure is directed to data storage systems and methodsthat include determining whether a write retry operation is requiredwhen a write head is off-track to a shingled side of a track in a bandof SMR medium. When there is no overlap or an off-track written sectoris not erased by the second track write operation, a write retryoperation is not performed.

More particularly, the present disclosure is directed to data storagesystems and methods that write data to an initial track in a band of aSMR medium, determine which side of the initial track is a shingledside, calculate a percentage of position error signal (PES) at ashingled side end of the initial track (PES1) when an off-track writeoperation occurs, and determine whether the percentage of PES1 at theshingled side end of the initial track meets a first pre-determinedthreshold. If the percentage of PES1 at the shingled side end of theinitial track is above the first pre-determined threshold, a re-writeoperation is performed to the track or media cache.

If the percentage of PES1 at the shingled side end of the initial trackis below the first pre-determined threshold, data is written to a secondtrack, the second track adjacent to the initial track. A percentage ofPES at the second track (PES2) is calculated at a shingled side end ofthe second track, and a determination is made as to whether a combinedvalue of PES1 and PES2 is above a second pre-determined threshold todetermine a probability value of the initial track being erased. If thecombined value of PES1 and PES2 is above the second pre-determinedthreshold, data is re-written to the initial track or media cache. Ifthe combined value of PES1 and PES2 is below the second pre-determinedthreshold, a writing operation may continue and new data is written to athird track. Thus, off-track write retry operations may be reduced.

As a result of the disclosed methods, there are improvements in adrive's performance under vibration, power consumption by reduction ofdisc retry operations, and hardware lifespan and noise level by reducingoverall mechanical movement.

The technology disclosed herein can be used with various data storagedevices. Examples of such data storage devices include hard disc drives.Other kinds of media are contemplated for use with the disclosedtechnology.

In the following description, reference is made to the accompanyingdrawing that forms a part hereof and in which are shown by way ofillustration at least one specific embodiment. In the drawing, likereference numerals are used throughout several figures to refer tosimilar components. In some instances, a reference numeral may have anassociated sub-label consisting of a lower-case letter to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification of a sub-label, the reference is intendedto refer to all such multiple similar components.

FIG. 1 is a block diagram of an example SMR data storage system 100,showing various functional components used to control the operation of adata storage device 110 (e.g., an SMR HDD, an SMR SSHD, an objectstorage device, etc.), including a schematic diagram of example shingledtracks in the SMR data storage system.

The data storage system 100 includes a computing or computing device 102(e.g., a computer, a mobile device, the internet, etc.) operablyconnected to the data storage device 110, each of the computing device102 and the data storage device 110 communicating with each other. Aprocessor 104 is located in the computing device 102. The processor 104sends one or more read or write commands to a storage device controller112 for execution. As control communication paths are provided betweenthe computing device 102 and the storage device controller 112, thestorage device controller 112 provides communication and control for thedata storage device 110.

A storage media 114 located in the data storage device 110 may be one ormore of a variety of tangible media (excluding carrier waves andcommunication signals), including hard disk drives. Other kinds of mediaare contemplated for use with the disclosed technology. The data storagedevice 110 further includes a cache 116 that is either a storage area onthe storage media 114 or another non-volatile memory accessible by thedata storage device 110. In the depicted system 100, the cache 116 is astorage area on the storage media 114.

A band (e.g., a band 120) of shingled tracks (e.g., an initial track nand a second track n+1) may also be located in the storage media 114. InFIG. 1, the shingled tracks n and n+1 are located in the band 120. Animplementation of the shingled tracks n and n+1 is arranged such thatwhen data is written to one of the shingled tracks n and n+1 (except forthe last data track), a writing operation affects data on an adjacenttrack in the shingled direction in a cross-track direction.

In SMR drives, to reduce write retry operations, data may be written toinitial track n in the band 120. The storage controller 112 candetermine which side of the initial track n is a shingled side. As shownin FIG. 1, the shingled side is side 130 of track n. When off-trackoccurs, the storage controller 112 calculates a percentage of positionerror signal (PES) at the shingled side end of the initial track n(PES1) with a PES module 108.

The storage controller 112 determines whether the PES1 is above a firstpre-determined threshold. For example, the first pre-determinedthreshold may be OCLIM+Δ. An OCLIM (on-cylinder limit) may be defined asthe off-track limit, which is pre-determined during drive design. Asshown in FIG. 1, in one example, the OCLIM has a 10% track pitch (TP).When a writer position from a track center (position error signals) isgreater than OCLIM, a writing operation may be stopped. In otherexamples, other drives may have different values for OCLIM.

If the PES1>OCLIM+Δ, or above the first predetermined threshold, thenthe affected sectors of the affected sectors may be rewritten to theinitial track n or alternatively, to media cache or NAND Flash. If thePES1<OCLIM+Δ, or below the first predetermined threshold, writeoperations continue when the off-track is to the shingled side and thePES1 is recorded at the end of the initial track n. A second track n+1is written, and the percentage of PES is calculated at the end of thesecond track n+1 (PES2).

If the Δ is defined to +2%, and if the PES1 at the shingled side end ofthe initial track n is greater than +12%, based on statistics, there isa higher probability that writing to the second track n+1 could erasesectors in the initial track n, and an immediate write retry isrequired. If the PES1 of an initial track n is greater than 10%, butless than 12%, based on statistics, there is a lower probability thatwriting to the second track n+1 will erase sectors of the initial trackn and there is no need to rewrite off-track sectors on track n.

In some implementations, although data does not need to be rewritten tothe previous track (initial track n), the PES may be recorded toaccelerate off-line error recovery. The Δ defined to +2% is an example,and the OCLIM is a factor in determining the probability that writing tothe second track n+1 could erase sectors in the initial track n,requiring a write retry operation. Specifically, the higher the value ofOCLIM, the higher the value of Δ.

When PES2 is calculated at a shingled side end of the second track n+1,a determination is made as to whether a combined value of PES1 and PES2is above a second pre-determined threshold to determine a probabilityvalue of the initial track n being erased. If the combined value of PES1and PES2 is above the second pre-determined threshold, data isre-written to the initial track n or media cache. If the combined valueof PES1 and PES2 is below the second pre-determined threshold, a writingoperation may continue and new data is written to a third track (notshown), the third track adjacent to the second track n+1.

For example, referring to FIG. 1, if the second predetermined thresholdis 20%, the PES1 at the shingled side end of the initial track n is+12%, and the OCLIM is 10%, if the PES2 to track n+1 is >−8% at the samelocation or servo wedge, there is a high probability that writing to thesecond track n+1 did not erase sectors of the initial track n. Thus, ifthe combined value of PES1 and PES2 is below 20%, a writing operationmay continue and new data is written to a third track.

In some implementations, when the off-track direction is distributedevenly, there may be approximately 50% chance to reduce write retryoperations. In overall, an SMR drive's performance can be improved,especially during a music test or other environment with disturbances.

FIG. 2 is a schematic diagram 200 of example shingled tracks in an SMRdata storage system. A storage controller (not shown) can determinewhich side of the initial track n is a shingled side and when off-trackoccurs, calculate a percentage of PES at the shingled side end of theinitial track n (PES1) with a PES module (not shown).

The storage controller determines whether the PES1 at the shingled sideend of the initial track n is above a first pre-determined threshold.For example, the first pre-determined threshold may be OCLIM+Δ. An OCLIM(on-cylinder limit) may be defined as the off-track limit, which ispre-determined during drive design. As shown in FIG. 1 the OCLIM has a10% track pitch (TP).

If the PES1>OCLIM+Δ, then the affected sectors may be rewritten to theinitial track n or alternatively, to media cache or NAND Flash. If thePES1<OCLIM+Δ, write operations continue when off-track to the shingledside and the PES1 is recorded at the end of the initial track n. Asecond track n+1 is written adjacent to the initial track n. Apercentage of PES is calculated at the end of the second track n+1(PES2).

When PES2 is calculated at a shingled side end of the second track n+1,a determination is made as to whether a combined value of PES1 and PES2is above a second pre-determined threshold to determine a probabilityvalue of the initial track n being erased. If the combined value of PES1and PES2 is above the second pre-determined threshold, data isre-written to the initial track n or media cache. If the combined valueof PES1 and PES2 is below the second pre-determined threshold, a writingoperation may continue and new data is written to a third track.

For example, referring to FIG. 2, if the second predetermined thresholdis 20%, the PES1 at the shingled side end of the initial track n is+12%, and the OCLIM is 10%, then writing to the second track n+1 coulderase sectors in the initial track n, if the PES2 to track n+1 is <−8%at the same location or servo wedge. Thus, if the combined value of PES1and PES2 is above 20%, data is re-written to the initial track n ormedia cache. Also, data will need to be rewritten to the shingledsectors on the second track n+1. Alternatively, data may be copied toother caching space, such as media cache or NAND Flash, to furtherimprove throughput.

FIG. 3 is a flowchart of example operations 300 for an improvedthroughput process in an SMR data storage system. An operation 302receives a write command to write data to an initial track in a band ofa shingled magnetic recording medium. An operation 304 determines whichside of the initial track is a shingled side.

An operation 306 calculates a percentage of position error signal (PES)at a shingled side end of the initial track (PES1) when an off-trackwrite operation occurs. An operation 308 determines whether thepercentage of PES1 at the shingled side end of the initial track isabove a first pre-determined threshold.

An operation 316 re-writes to the track or media cache responsive todetermining the percentage of PES1 at the shingled side end of theinitial track is above the first pre-determined threshold. Afteroperation 316, operation 306 may occur again.

An operation 310 writes data to a second track responsive to determiningthe percentage of PES1 is below the first pre-determined threshold. Thesecond track is adjacent to the initial track. An operation 312calculates a percentage of PES at the second track (PES2) when anoff-track write operation occurs and an operation 314 determines whethera combined value of PES1 and PES2 is above a second pre-determinedthreshold to determine a probability value of the initial track beingerased.

An operation 316 re-writes to the initial track or media cacheresponsive to determining the combined value of PES1 and PES2 is abovethe second pre-determined threshold. An operation 318 writes data to athird track adjacent to the second track responsive to determining thecombined value of PES1 and PES2 is below the second pre-determinedthreshold.

FIG. 4 illustrates a block diagram 400 of an example computer systemsuitable for implementing methods and systems of reducing off-trackwrite retry operations in shingled magnetic recording systems disclosedherein. The computer system 400 is capable of executing a computerprogram product embodied in a tangible computer-readable storage mediumto execute a computer process. Data and program files may be input tothe computer system 400, which reads the files and executes the programstherein using one or more processors. Some of the elements of a computersystem 400 are shown in FIG. 4 wherein a processor 402 is shown havingan input/output (I/O) section 404, a Central Processing Unit (CPU) 406,and a memory section 408. There may be one or more processors 402, suchthat the processor 402 of the computing system 400 comprises a singlecentral-processing unit 406, or a plurality of processing units. Theprocessors may be single core or multi-core processors. The computingsystem 400 may be a conventional computer, a distributed computer, orany other type of computer. The described technology is optionallyimplemented in software loaded in memory 408, a disc storage unit 412 orremovable memory 418.

In an example implementation, the disclosed system and methods may beembodied by instructions stored in memory 408 and/or disc storage unit412 and executed by CPU 406. Further, local computing system, remotedata sources and/or services, and other associated logic representfirmware, hardware, and/or software which may be configured toadaptively distribute workload tasks to improve system performance. Thedisclosed methods may be implemented using a general purpose computerand specialized software (such as a server executing service software),and a special purpose computing system and specialized software (such asa mobile device or network appliance executing service software), orother computing configurations. In addition, program data, such asdynamic allocation threshold requirements and other information may bestored in memory 408 and/or disc storage unit 412 and executed byprocessor 402.

For purposes of this description and meaning of the claims, the term“memory” means a tangible data storage device, including non-volatilememories (such as flash memory and the like) and volatile memories (suchas dynamic random access memory and the like). The computer instructionseither permanently or temporarily reside in the memory, along with otherinformation such as data, virtual mappings, operating systems,applications, and the like that are accessed by a computer processor toperform the desired functionality. The term “memory” expressly does notinclude a transitory medium such as a carrier signal, but the computerinstructions can be transferred to the memory wirelessly.

The embodiments described herein are implemented as logical steps in oneor more computer systems. The logical operations of the embodimentsdescribed herein are implemented (1) as a sequence ofprocessor-implemented steps executing in one or more computer systemsand (2) as interconnected machine or circuit modules within one or morecomputer systems. The implementation is a matter of choice, dependent onthe performance requirements of the computer system implementingembodiments described herein. Accordingly, the logical operations makingup the embodiments described herein are referred to variously asoperations, steps, objects, or modules. Furthermore, it should beunderstood that logical operations may be performed in any order, unlessexplicitly claimed otherwise or a specific order is inherentlynecessitated by the claim language.

The above specification, examples, and data provide a completedescription of the structure and use of example embodiments describedherein. Since many alternate embodiments can be made without departingfrom the spirit and scope of the embodiments described herein, theinvention resides in the claims hereinafter appended. Furthermore,structural features of the different embodiments may be combined in yetanother embodiment without departing from the recited claims. Theimplementations described above and other implementations are within thescope of the following claims.

What is claimed is:
 1. A method comprising: receiving a write command to write data on an initial track in a band of a shingled magnetic recording medium; calculating a percentage of position error signal (PES) of the initial track (PES1); determining whether the percentage of PES1 meets a first pre-determined threshold; and writing data to a second track responsive to determining the percentage of PES1 is below the first pre-determined threshold, the second track being adjacent to the first track in the shingled direction.
 2. The method of claim 1, further comprising: determining which side of the band is a shingled side; and calculating the PES1 at a shingled side end of the initial track when an off-track write operation occurs.
 3. The method of claim 1, further comprising: re-writing data to a media cache responsive to determining the PES1 is above the first pre-determined threshold.
 4. The method of claim 1, further comprising: re-writing data to the initial track responsive to determining the PES1 above the first pre-determined threshold.
 5. The method of claim 1, further comprising: calculating a percentage of PES at a shingled side end of the second track (PES2); and determining whether a combined value of PES1 and PES2 is above a second pre-determined threshold to determine a probability value of the initial track being erased.
 6. The method of claim 5, further comprising: re-writing data to the initial track responsive to determining a combined value of PES1 and PES2 is above a second pre-determined threshold.
 7. The method of claim 5, further comprising: re-writing data to a media cache responsive to determining a combined value of PES1 and PES2 is above a second pre-determined threshold.
 8. A system, comprising: a position error signal (PES) module configured to calculate a percentage of PES of an initial track in a band in a shingled magnetic recording medium (PES1); and a storage controller configured to: determine whether the PES1 meets a first pre-determined threshold; and write data to a second track responsive to determining the PES1 is below the first pre-determined threshold, the second track being adjacent to the first track.
 9. The storage device system of claim 8, wherein the PES module is configured to calculate the PES1 at a shingled side end of the initial track when an off-track write operation occurs.
 10. The storage device system of claim 8, wherein the storage controller is further configured to: re-write data to a media cache responsive to determining the PES1 is above the first pre-determined threshold.
 11. The storage device system of claim 8, wherein the storage controller is further configured to: re-write data to the initial track responsive to determining the PES1 is above the first pre-determined threshold.
 12. The storage device system of claim 8, wherein the storage controller is further configured to: calculate a percentage of PES at the second track (PES2) at a shingled side end of the second track; and determine whether a combined value of PES1 and PES2 is above a second pre-determined threshold to determine a probability value of the initial track being erased.
 13. The storage device system of claim 12, wherein the storage controller is further configured to: re-write data to media cache responsive to determining the combined value of PES1 and PES2 is above a second pre-determined threshold.
 14. The storage device system of claim 13, wherein the storage controller is further configured to: re-write data to the initial track responsive to determining the combined value of PES1 and PES2 is above a second pre-determined threshold.
 15. One or more tangible computer-readable storage media encoding computer-executable instructions for executing on a computer system a computer process, the computer process comprising: receiving a write command to write data on an initial track in a band of a shingled magnetic recording medium; calculating a percentage of position error signal (PES) of the initial track (PES1); determining whether the PES1 meets a first pre-determined threshold; and writing to a second track responsive to determining the PES1 is below the first pre-determined threshold, the second track being adjacent to the first track.
 16. The one or more tangible computer-readable storage media of claim 15, further comprising: determining which side of the initial track is a shingled side; and calculating a PES1 at a shingled side end of the initial track when an off-track write operation occurs.
 17. The one or more tangible computer-readable storage media of claim 15, further comprising: re-writing data to media cache responsive to determining the PES1 is above the first pre-determined threshold.
 18. The one or more tangible computer-readable storage media of claim 15, further comprising: re-writing data to the initial track responsive to determining the PES1 is above the first pre-determined threshold.
 19. The one or more tangible computer-readable storage media of claim 15, further comprising: calculating a percentage of PES at the second track (PES2) at a shingled side end of the second track; and determining whether the PES1 and the PES2 are above a second pre-determined threshold to determine whether the initial track is erased.
 20. The one or more tangible computer-readable storage media of claim 19, further comprising: re-writing data to the initial track responsive to determining the combined value of PES1 and PES2 is above a second pre-determined threshold. 